The present invention relates to a pulse width modulation decoder.
Pulse width modulation (hereinafter, referred to as "PWM") is a method of encoding a sequence of numerical values by modulating the duty cycle of a fixed-frequency square-wave carrier signal. More specifically, the duty cycle of each successive period of the carrier signal is modulated in proportion to its corresponding numerical value in the sequence. Typically, the information represented by the sequence of numerical values is either a succession of distinct measurement results or periodic samples of a continuous waveform.
The purpose of a PWM decoder is to recover the originally encoded sequence of numerical values from the modulated signal, typically by successive generation of a proportional analog signal based on the sequence of numerical values. One known PWM decoder includes a resistor-capacitor integrator circuit and a PWM decoder/encoder applied to a digital control apparatus, thereby interfacing with a controlled object. This will be described with reference to the attached drawings.
FIG. 1 is a controlling circuit using a PWM signal. In FIG. 1, a microcomputer 1 is a PWM signal source. An integrator 2 consisting of a diode D1, two resistors R1 and R2, and three capacitors C1, C2 and C3 demodulates a PWM signal, producing a linear analog signal. A signal processor 3 receives the output of the integrator 2 to drive a controlled object (not shown). Here, when driving the controlled object, the signal processor 3 has a slope characteristic different from that of the PWM signal. Therefore, it is necessary for the purpose of providing a compatible slope characteristic between the linear analog signal and the object to be controlled by the signal processor 5 that either the PWM signal from the microcomputer 1 to have an identical slope characteristic of the controlled object, or the demodulation characteristic of the integrator 2 to have a slope characteristic of the controlled object in order to provide proper interface with the signal processor 3 for driving the controlled object effectively.
However, the conventional microcomputer uses complex circuits to generate a proper PWM signal. Also, conventional integrators used in demodulating the PWM signal are linear and the microcomputer can not precisely control an object whose operational characteristics are of a different slope.